Valuable heavy minerals from the Brahmaputra River sands of Northern Bangladesh

Abstract

The sands of Bangladesh's rivers are potentially economically important hosts for heavy mineral (HM) resources. Characterisation tests carried out by the authors on 50 sand samples collected from sand bars of the Brahmaputra River in northern Bangladesh revealed that the HM assemblage of the predominantly quartz-rich sands ranged from 4.5 to 17.0% (by weight) HM. The HM assemblage of the samples tested predominantly comprised amphibole, epidote, garnet, kyanite and feldspars along with minor amounts of the valuable heavy mineral (VHM) components of ilmenite, magnetite, rutile and zircon. The HMs were generally well liberated and had an angular to sub-round texture. A grain size analysis of a composite sample prepared from a subset of 7 of the 50 samples collected indicated that >75% of the total HM assemblage was within the +250 to −125 µm size fraction with VHMs enriched in the size fractions −250 to +125 µm and −125 to +63 µm. The total HM contents in the coarser −500 to +250 µm size fraction and the finer −63 µm size fractions were negligible. The potentially recoverable VHM components of the composite included magnetite (∼3%), ilmenite (∼4%), titanite (∼1%), titanomagnetite (∼1%), zircon (∼0.5%) and rutile (∼0.4%). Preliminary laboratory separation studies on a bulk sample indicated that magnetite-, ilmenite-, rutile- and zircon-rich concentrates could be prepared from the sands. Analyses of the ilmenite indicated that the ilmenite was primary in composition (∼34% Ti), low in detrimental impurities and would be suitable for pigment production via the sulphate processing route. The zircon and rutile components were also low in total impurities and as such, little or no further processing would be required to produce saleable concentrates of these VHMs. However, the magnetite concentrate was contaminated by composite magnetite/silicate particles and further work involving fine grinding would be required to liberate the magnetite particles and generate a magnetite-rich product.